The present invention relates to a power transmission control device, a power transmitting device, an electronic instrument, a non-contact power transmission system, and the like.
In recent years, non-contact power transmission (contactless power transmission) that utilizes electromagnetic induction to enable power transmission without metal-to-metal contact has attracted attention. As application examples of non-contact power transmission, charging a portable telephone, charging a household appliance (e.g., cordless telephone handset), and the like have been proposed.
JP-A-2006-60909 discloses related-art non-contact power transmission. According to the technology disclosed in JP-A-2006-60909, data is transmitted from a power receiving device (secondary-side instrument) to a power transmitting device (primary-side instrument) by means of load modulation. The power transmitting device detects the induced voltage of the primary coil using a comparator or the like to detect a change in power-receiving-side (secondary-side) load state due to insertion of a foreign object or data transmission.
According to the technology disclosed in JP-A-2006-60909, the power-receiving-side load state is detected by comparing the peak voltage of the induced voltage with a given threshold voltage. However, the threshold voltage used to determine the detected voltage varies due to a change in power supply voltage, a change in the distance/positional relationship between the primary coil and the secondary coil, a change in element constant (e.g., coil inductance), or the like. This makes it difficult to correctly detect the power-receiving-side load state.